The prior art is replete with examples of composite structure constructions employing composite slab and joist assemblies. In many of these examples, the slabs of concrete are positioned on the joists, and, during construction, to support the newly-poured unset concrete that will become parts of the slabs, forms for the concrete are mounted between adjacent joists of the assemblies.
Butts et al. (U.S. Pat. No. 3,845,594) discloses an example of a composite slab and joist assembly in which the forms for the unset concrete are made of plywood. After the concrete hardens, the plywood is removed and reused.
Other methods of forming composite slab and joist assemblies employ metal deck panels for concrete forms in place of wood, and the deck panels remain as parts of the assemblies. When metal deck panels are used, labor for removing wooden forms is unnecessary, and, by not using wood to construct the composite slab and joist assemblies, the number of trades required for the construction is fewer. Thus, constructing the assemblies using metal deck panels eliminates some of the labor costs.
Person et al. (U.S. Pat. No. 4,700,519) discloses an example of a composite slab and joist assembly employing metal deck panels. With reference to the perspective view of FIG. 1 and the corresponding cross-section in FIG. 2, a composite slab and joist assembly 100 typically includes a slab 104 and a plurality of joists 108. Slab 104 may be formed of concrete with reinforcement, such as reinforcing steel mesh 112, enclosed therein. Each joist 108 includes a bottom chord 116, a top chord 120, and an open web 124 affixed therebetween, and web 124 typically comprises a series of adjacent triangulating compression and tension members 128.
FIGS. 1 and 2 show that both bottom chord 116 and top chord 120 comprise two elongated structural angles 132,136 and 140,144, respectively. Structural angles are sometimes referred to as “angle bars.” Structural angles are readily-available commodities, which may be cold-formed or hot-rolled.
In the example of FIGS. 1 and 2, structural angles 132,136 of bottom chord 116 are oriented so that each has in cross-section an upwardly-extending leg 148,152 and a horizontally-extending leg 156,160 meeting at a corner 164,168. Structural angles 132,136 are joined in a parallel relationship at the same height to opposite sides of web 124. Web 124 joins structural angles 132,136 along the surfaces of upwardly-extending legs 148,152. Structural angles 132,136 are situated such that horizontally-extending legs 156,160 extend outwardly from web 124.
As shown also in the FIG. 3 close-up of a cross-section of top chord 120, structural angles 140,144 are also oriented so that each has, in cross-section, an upwardly-extending leg 172,176 and a horizontally-extending leg 180,184 meeting at a corner 188,192. Unlike in bottom chord 116, however, the top chord 120 upwardly-extending legs 172,176 are directly joined “back-to-back” without web 124 positioned therebetween. Instead, web 124 is joined below at junction 196 adjacent corners 188,192. As with bottom chord 116, structural angles 140,144 of top chord 120 are situated such that horizontally-extending legs 180,184 extend outward from corners 188,192.
To form assembly 100, a plurality of joists 108 are spaced apart on supporting members, such as building girders, beams, or walls, and deck panels 200, typically formed of rolled corrugated steel, are positioned therebetween. As shown in FIGS. 1 and 2, deck panels 200 are supported at opposite edges by horizontally-extending legs 180,184 of top chords 120. Such an arrangement facilitates the proper horizontal spacing of joists 108 on the supporting members. Deck panels 200 are then secured to top chords 120.
Reinforcing mesh 112 is placed on deck panels 200. As shown also with reference to FIGS. 1 and 2, upwardly-extending legs 172,176 of top chords 120 act as “high-chairs” to raise mesh 112 to a higher position directly above joists 108. With mesh 112 in place, concrete is poured thereon and on deck panels 200 to form slab 104 of composite slab and joist assembly 100.
As is apparent in FIGS. 1–3, structural angles 140,144 of top chord 120 are not identical in dimension, because upwardly-extending leg 176 of structural angle 144 extends higher than upwardly-extending leg 172 of structural angle 140. The reason for this configuration is that upwardly-extending leg 176 has a series of transverse concrete-engaging deformations 204, which act as sheers connector to transfer compression forces from top chord 120 to concrete slab 104. Accordingly, with this configuration, upwardly-extending leg 176 of structural angle 144 must extend upward beyond the upper extant of upwardly-extending leg 172.
Referring in particular to FIGS. 2 and 3, it is apparent that the surface area is limited at junction 196 for butt-welding web 124 to top chord 120. Accordingly, such a configuration limits the surface area available for the welded connection.
Dutil (U.S. Pat. No. 5,544,464) discloses a configuration that overcomes this problem. As shown in FIGS. 4 and 5, a joist 208 has a top chord 212, which includes a structural element 216 with a upwardly-extending segment 220 that offers a greater surface area for joining to a web 224. Structural element 216 also has a horizontally-extending leg 228 for supporting an edge 232 of a deck panel 236.
For joist 208 to support an edge 232 of a deck panel 236 on the opposite side from structural element 216, a structural angle 240 is added so that structural element 216 aid structural angle 240 enclose the top of web 224 therebetween. However, for welding structural angle 240 to web 224, access is limited due to the positioning of structural element 216. Consequently, it is difficult to weld structural angle 240 sufficiently to develop its working capacity beyond supporting a deck panel 236. Also, additional reinforcement of top chord 212 may be necessary to reinforce joist 208 during the non-composite stage (before the concrete sets), thus requiring more material and additional formation steps. For example, the top chord may be reinforced by welding steel to the “S”-shaped section.
Accordingly, to the best knowledge of the present inventors, there is an unmet need for an economical composite slab and joist assembly in which the joist top chords have segments which extend vertically into the concrete slab and simultaneously have segments that extend vertically, whether upwardly or downwardly, offering expanded surface area for joining to joist webs in such a configuration with sufficient access for attachment of the webs to the corresponding top chords to thereby develop greater working capacity, that is, greater ability to support loads over the life of the structure.